1. Field of the Invention
The invention relates to catalysts and more particularly to acidic cation exchange resins used as catalysts to promote condensations of ketones with phenol compounds.
2. Brief Description of the Prior Art
Acidic cation exchange resins have been employed to catalyze the condensation of ketones with phenols for a number of years; see for example the early description found in U.S. Pat. No. 3,242,219. In more recent years, improvements to the catalyst have included chemical modification. The modifications generally involve covalent or ionic attachment of an organic mercaptan species ("promoter") to the resin which provides enhanced reaction activity or selectivity relative to the unmodified resin. For example, the U.S. Pat. No. 4,294,995 (incorporated herein by reference thereto) describes a sulfonated polystyrene ion-exchange resin having organo mercaptan promoter groups attached to the backbone sulfone radicals by covalent nitrogen-sulfur linkages. Representative of other resins modified in this manner are those described in U.S. Pat. 3,394,089; 3,634,341; 4,294,995; 4,346,247; 4,400,555; 4,424,283; 4,584,416; 5,075,511; all of which are incorporated herein by reference thereto.
Unfortunately, the catalytic activity and selectivity of the cation exchange catalysts modified to attach a mercaptan promoter is often lost after varying periods of use. Deactivation can occur in as short a time as 2 to 6 weeks depending on several factors, including promoter type and flow rates (production rates) through the resin. This is a particular problem, when the catalyst is employed in the commercial preparation of bisphenol-A by the condensation of acetone with phenol. The active sites of the catalyst may become blocked with organic tars incident to the condensation or chemically modified. The resin must be replaced or regenerated causing significant expense, process complication, and downtime. Regeneration, when possible, often involves treatment with an aqueous strong acid to remove the promoter and tarry by-products.(see for example the method of U.S. Pat. No. 4,051,079), followed by reattachment of fresh promoter.
The ideal solution to solving the problem of catalyst deactivation is to delay or prevent blocking of the promoter site. We have now found a method of preventing or reducing the rate of deactivation without interrupting the use of the catalyst in processes for the condensation reactions it is employed to catalyze.
Advantages of the method of the invention include the elimination of catalyst regeneration and extension of time periods between catalyst regenerations (a large capital investment). Studies reveal the product selectivity is not adversely affected by the method of the invention.